THE STRUCTURE OF THE BRAIN STEM 



379 



The fibres of each are derived from ganglion-cells in the internal ear, pass to 

 the medulla at its widest part and then, dividing into two, terminate in 

 masses of grey matter situated at the extreme lateral part of the floor of the 

 fourth ventricle. 



The branches of the cochlear nerve (Fig. 193) make connection with two 

 collections of cells, the dorsal nucleus, apparently embedded in the fibres of 

 the root itself, and the accessory nucleus, a little triangular mass of grey 

 matter situated in the angle between the cochlear and vestibular nerves. 



TO VERMIS 



TO HEMISPHERE 



FIBRES OF 



VESTIBULAR 



ROOT 



NERVE 

 ENDINGS 

 IN MACUL/E 

 &AMPULUE 





FIG. 194. Plan of the course and connections of the fibres forming the vestibular 



root of the auditory nerve. (SCHAFEB.) 



r, restiform body ; v, descending root of fifth nerve; p. cells of principal nucleus 

 of vestibular root ; d, fibres of descending vestibular root ; nd, a cell of the descend- 

 ing vestibular nucleus ; D, cells of nucleus of Deiters ; B, cells of nucleus of Bech- 

 terew ; nt, cells of nucleus tecti (fastigii) of the cerebellum ; plb, fibres of posterior 

 longitudinal bundle. No attempt has been made in this diagram, to represent the 

 actual positions of the several nuclei. Thus a large part of Deiters' nucleus lies 

 dorsal to and in the immediate vicinity of the restiform body. 



From these nuclei fibres are given off which take two courses. Some, follow- 

 ing the previous course of the cochlear nerve, pass across the surface of the 

 fourth ventricle as the strice medullares or stria, acousticce, and then bending 

 inwards pass into the tegmentum of the opposite side. Others pass deeply 

 and form a mass of transverse fibres in the ventral part of the tegmentum, the 

 corpus trapezoides or trapezium. After making connections with the superior 

 olivary body and a special nucleus, they join the superficial set of fibres, and 

 run up in the tegmentum to the inferior corpora quadrigemina, forming the 

 lateral fillet. 



The vestibular nerve (Fig. 194) also has two nuclei of termination, the 

 median nucleus with small cells, and the lateral or Deiters' nucleus with large 

 cells. Some fibres pass also to the nucleus of Bechterew, which is in close 

 relation with the roof nuclei of the cerebellum. The descending fibres end 

 chiefly in the median nucleus, while the ascending fibres end in Deiters' 



